package com.cr4y0n.hot100;

/**
 * @author cr4y0n
 * <a href="https://leetcode.cn/problems/merge-two-sorted-lists/description/?envType=study-plan-v2&envId=top-100-liked">合并两个有序链表</a>
 * 将两个升序链表合并为一个新的 升序 链表并返回。新链表是通过拼接给定的两个链表的所有节点组成的。
 * 示例 1：
 * 输入：l1 = [1,2,4], l2 = [1,3,4]
 * 输出：[1,1,2,3,4,4]
 * 示例 2：
 * 输入：l1 = [], l2 = []
 * 输出：[]
 * 示例 3：
 * 输入：l1 = [], l2 = [0]
 * 输出：[0]
 */
public class _21_MergeTwoSortedLists {
    public static class ListNode {
        int val;
        ListNode next;

        ListNode() {
        }

        ListNode(int val) {
            this.val = val;
        }

        ListNode(int val, ListNode next) {
            this.val = val;
            this.next = next;
        }
    }

    static class Solution {
        public ListNode mergeTwoLists(ListNode list1, ListNode list2) {
            if (list1 == null && list2 == null) {
                return list1;
            }
            ListNode dummy = new ListNode(0);
            ListNode cur = dummy;
            while (list1 != null && list2 != null) {
                if (list1.val <= list2.val) {
                    cur.next = list1;
                    list1 = list1.next;
                } else {
                    cur.next = list2;
                    list2 = list2.next;
                }
                cur = cur.next;
            }
            if (list1 != null) {
                cur.next = list1;
            }
            if (list2 != null) {
                cur.next = list2;
            }
            return dummy.next;
        }
    }
}
